The present invention relates to a spin dryer for centrifugally removing a liquid material from a substrate such as a semiconductor wafer or a glass substrate for LCD (liquid crystal display device) so as to dry the substrate surface and also relates to a substrate drying method.
In the manufacture of a semiconductor device, a semiconductor wafer is subjected to washing with chemicals and water, followed by drying the wafer so as to cleanse the wafer surface. Used in the drying step is a spin dryer disclosed in, for example, U.S. Pat. No. 5,435,075, Japanese Utility Model Disclosure (Kokai) No. 63-180925, Japanese Patent Disclosure No. 7-17651, and Japanese Patent Disclosure No. 6-97148.
When it comes to the spin dryer disclosed in U.S. Pat. No. 5,435,075, it is necessary to introduce a drying air effectively into the cradle and to distribute efficiently the introduced drying air into spaces between adjacent wafers in order to bring the drying air into contact sufficiently and uniformly with each wafer. Also, dusts generated from a driving source of the cradle and the peripheral equipment and particles generated by static charging are likely to be contained in the drying air, with the result that these particles are attached to the wafer in the drying step so as to bring about a wafer contamination problem. Further, it is possible for the air discharged through an outlet port of the drying chamber to flow backward into the drying chamber, with the result that the particles contained in the discharged air are likely to be attached to the wafer.
In the spin dryer disclosed in Japanese Utility Model Disclosure No. 63-180925, a pair of box-shaped cassette holders are rockably supported by a pair of frame walls erected on a rotor. The spin dryer is constructed to permit these cassette holders to be moved away from or toward each other. In this apparatus, cassettes each housing a large number of wafers are inserted into the paired cassette holders, followed allowing these cassette holders to be moved away from each other. Then, when the rotor is rotated under this condition, the cassette holders assume a horizontal posture so as to permit the liquid material attached to the wafer to be centrifugally removed from the wafer surface. In this apparatus, however, the wafers after the washing treatment are inserted together with the cassette into cassette holder. Naturally, the cassette holder occupies a larger volume, leading to enlargement of the drying apparatus. In addition, the cassette is also dried together with the wafers, leading to a longer time required for the drying operation. Further, since the cassette is inserted into the cassette holder, the flow of the drying air is disturbed, leading to a lower drying efficiency. Still further, the disturbance of the drying air flow causes the particles to be more likely to be attached to the wafers, leading to the wafer contamination problem.
The apparatus disclosed in Japanese Patent Disclosure No. 7-176512 comprises a mount (cassette) for holding wafers transferred by a transfer arm and a box-shaped cradle for housing the mount (cassette). The cradle is equipped with a holding member for holding the mount in a lower position of the wafers and with another holding member for holding the mount in the central position of the wafers. Since the mount in place of a cassette is put in the box-shaped cradle, the volume occupied by the cradle is diminished, leading to miniaturization of the drying apparatus. However, since the cradle is in the shape of a box, a drying air flowing within the cradle is disturbed, leading to a low drying efficiency. In addition, the disturbance of the drying air flow causes particles to be attached to the wafer, leading to a wafer contamination problem.
Further, the apparatus disclosed in Japanese Patent Disclosure No. 6-97148 comprises a pair of inclinable cradles positioned to face each other and a horizontal holding mechanism for horizontally holding these cradles. Also, holding mechanisms for holding the peripheral portions of the wafer are mounted to the side walls of each of these cradles so as to prevent the wafers from being dropped during rotation of the cradle. However, the wafer holding mechanism included in the apparatus disclosed in this prior art is considerably complex in construction. Also, since a spring force is utilized for holding the wafer, the contact area between the holding member and the wafer is increased. It follows that a foreign matter is likely to be attached to the wafer, giving rise to contamination of the wafer. Further, where the pushing force of the spring is excessively large, the wafer is likely to be deformed.
What should also be noted is that, in the conventional spin dryer, it is necessary to lessen the impact received by the wafer during rotation of the cradle at a high speed so as to prevent the damage done to the wafer.